Exhaust treatment control system for an internal combustion engine

ABSTRACT

The present invention relates to an engine exhaust treatment system ( 20 ) including a first exhaust gas path ( 24 ) having a diesel particulate filter ( 32 ) and a second exhaust gas path ( 26 ) having a catalytic converter ( 34 ). The system also includes a valve arrangement ( 36, 38 ), for controlling exhaust gas flow between the first and second paths ( 24, 26 ). The system ( 20 ) further includes a controller ( 40 ) for sensing/monitoring operating conditions of the engine ( 22 ) and the condition of the diesel particulate filter ( 32 ). The controller ( 40 ) shifts exhaust gas flow between the first and second paths ( 24, 26 ) based on the operating condition of the engine ( 22 ) and/or the condition of the diesel particulate filter ( 32 ) to optimize filtration efficiency while preventing unacceptable levels of backpressure and detrimental regeneration of the filter ( 32 ).

This application is being filed as a PCT international patentapplication in the name of Donaldson Company, Inc., a U.S. nationalcorporation (applicant for all designations except the U.S.), and in thenames of Wayne M. Wagner, Edward A. Steinbrueck, and Julian A. Imes, allcitizens and residents of the U.S. (applicants for the U.S. designationonly), on 25 Oct. 2002, designating all countries.

FIELD OF THE INVENTION

The present invention relates generally to exhaust treatment systemshaving cores such as catalytic converters or diesel particulate filters.

BACKGROUND OF THE INVENTION

To reduce air pollution, vehicle emissions standards have becomeincreasingly more stringent. With respect to both internal combustionand diesel engines, catalytic converters have been used to reduce theconcentration of pollutant gases (e.g., hydrocarbons, carbon monoxide,nitrogen oxides, etc.) in the exhaust stream. Also, with respect todiesel engines, diesel particulate filters have been used to reduce theconcentration of particulate matter (e.g., soot) in the exhaust stream.

A typical catalytic converter includes a substrate mounted in an outercasing or “can.” The substrate defines a plurality of longitudinalchannels that extend through the catalytic converter. Exemplarysubstrate materials include ceramic (e.g., extruded magnesia aluminasilicate) and corrugated metal (e.g., stainless steel). A catalyst isprovided on the substrate for promoting the oxidation of a gaseouspollutant. For example, the catalyst can include a precious metal suchas platinum, palladium or rhodium, a base metal or a material such aszeolite. In some cases, a material such as zeolite can be included asboth a substrate and a catalyst.

A typical diesel particulate filter includes a ceramic substrate mountedin an outer casing. The ceramic substrate is porous and defines aplurality of longitudinal channels. Adjacent longitudinal channels areplugged at opposite ends of the core as described in U.S. Pat. No.4,851,015 that is hereby incorporated by reference in its entirety. Theplugged ends forces exhaust gases to flow through the walls of thesubstrate so that soot is collected on the walls as the gases passtherethrough. For some applications, a catalyst can be provided on thesubstrate such that the filter functions like a catalytic converter toreduce the concentration of pollutant gases.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to an engine exhausttreatment system including a first exhaust gas path having a dieselparticulate filter and a second exhaust gas path having a catalyticconverter. The system also includes a valve arrangement for controllingexhaust gas flow between the first and second paths. The system furtherincludes a controller for sensing/monitoring operating conditions of theengine and the condition of the diesel particulate filter. Thecontroller shifts exhaust gas flow between the first and second pathsbased on the operating condition of the engine and/or the condition ofthe diesel particulate filter.

A variety of other aspects of the invention are set forth in part in thedescription that follows, and in part will be apparent from thedescription, or may be learned by practicing the invention. The aspectsof the invention relate to individual features as well as combinationsof features. It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exhaust treatment system constructed in accordance withthe principles of the present invention;

FIG. 2 is a particulate mass reduction efficiency graph corresponding tothe system of FIG. 1;

FIG. 3 is a further exhaust treatment system constructed in accordancewith the principles of the present invention, the system includesstructure for reducing nitrogen oxide emissions;

FIG. 4 is a passive filter regeneration exhaust treatment systemconstructed in accordance with the principles of the present invention;

FIGS. 5A-5L show example flow logic for controlling the system of FIG.4;

FIG. 6A shows an exhaust system packing arrangement that is anembodiment of the present invention, the view is a longitudinalcross-section of the system;

FIG. 6B is a cross-sectional view taken along section line 6B-6B of FIG.6A;

FIG. 6C shows an alternative packing arrangement that is an embodimentof the present invention;

FIG. 7 shows a multi-filter exhaust system that is an embodiment of thepresent invention;

FIG. 8A shows an exhaust system packing arrangement corresponding to thesystem of FIG. 7, the view is a longitudinal cross-section of thesystem;

FIG. 8B is a cross-sectional view taken along section line 8B-8B of FIG.8A; and

FIG. 8C shows an alternative packing arrangement that is an embodimentof the present invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION

In the following detailed description, references are made to theaccompanying drawings that depict various embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

I. System With Active Filter Regeneration

FIG. 1 illustrates an exhaust treatment system 20 in accordance with theprinciples of the present invention. The system is adapted for use intreating the exhaust emissions of a diesel engine 22 such as the dieselengine of a vehicle (e.g., a truck, bus or off-road vehicle). The system20 includes a first exhaust gas pathway 24 and a second exhaust gaspathway 26. The pathways 24, 26 direct gases emitted from the engine 22to outlets 28 and 30. A diesel particulate filter 32 (DPF) is positionedalong the first gas pathway 24 and a catalytic converter 34 (DOC) ispositioned along the second gas pathway 26. Valves 36 and 38 control gasflow from the engine 22 to the first and second gas pathways 24, 26. Acontroller monitors the operating condition of the engine 22 and theoverall system 20, and also controls operation of the valves 36, 38.Depending on the operating condition of the engine 22 and the overallsystem 20, the controller causes the valves 36 and 38 to direct flow toeither the first gas path 24 or the second gas flow path 26. In certainembodiments, the controller 40 can selectively proportion flow to bothflow paths 24, 26 to control backpressure and optimize the particulatematter mass reduction efficiency of the system.

The diesel particulate filter 32 can have a variety of knownconfigurations. An exemplary configuration includes a monolith ceramicsubstrate having a “honey-comb” configuration of plugged passages asdescribed in U.S. Pat. No. 4,851,015 that is hereby incorporated byreference in its entirety. In certain embodiments, the substrate caninclude a catalyst. Exemplary catalysts include precious metal catalystssuch as platinum, palladium or rhodium, or other types of catalysts suchas base metals or zeolites.

The diesel particulate filter 32 preferably has a particulate massreduction efficiency greater than 75%. More preferably, the dieselparticulate filter has a particulate mass reduction efficiency greaterthan 85%. Most preferably, the diesel particulate filter 34 has aparticulate mass reduction efficiency equal to or greater than 90%. Forpurposes of this specification, the particulate mass reductionefficiency is determined by subtracting the particulate mass that entersthe filter from the particulate mass that exits the filter, and bydividing the difference by the particulate mass that enters the filter.

The catalytic converter 34 can have a variety of known configurations.Exemplary configurations include substrates defining channels thatextend completely therethrough. Exemplary catalytic converterconfigurations having both corrugated metal and ceramic substrates aredescribed in U.S. Pat. No. 5,355,973, that is hereby incorporated byreference in its entirety. The substrates preferably include a catalyst.For example, the substrate can be made of a catalyst, impregnated with acatalyst or coated with a catalyst. Exemplary categories of catalystsinclude carbon monoxide (CO) catalysts, hydrocarbon (HC) catalysts, leanNOx (oxides of nitrogen such as nitric oxide) catalysts and selectivereduction catalysts. Exemplary catalysts include precious metalcatalysts such as platinum, palladium or rhodium, or other types ofcatalysts such as base metals or zeolites.

The catalytic converter 34 typically will have a reduced particulatereduction efficiency as compared to the filter 32. In one embodiment,the catalytic converter 34 has a particulate mass reduction efficiencyless than 50% or less than 40%. In one embodiment, the particulate massreduction efficiency for the catalytic converter 34 is about 30%.

Referring still to FIG. 1, the system 20 includes a heating element 42for heating the filter 32 to regenerate the filter 32 by burning offexcess soot. The heating element 42 can have a variety of configurationssuch as an electric heater, a burner such as a diesel fuel burner, or aninjector for injecting fuel into the filter 32 to promote oxidation ofthe soot. A typical diesel fuel burner includes a chamber is whichdiesel fuel is injected and ignited. Hot exhaust gas from the chambercan be used to burn the soot on the filter. In some embodiments, an airinjector is provided upstream of the heating element 42 (see U.S. Pat.No. 4,851,015 that was previously incorporated by reference) to providea controlled amount of oxygen to the filter 32 to support combustion ofthe soot.

The controller 40 of the system interfaces with a pressure sensor 46that measures the pressure on the upstream side of the filter 32 and apressure sensor 49 that measures the pressure at the downstream side ofthe filter. Data from these sensors can be used to determine the loadingof the filter. In certain embodiments, the downstream side of the filter32 can be assumed to be at atmospheric pressure thereby eliminating theneed for sensor 49.

The controller 40 can also interface with a pressure sensor 47 locatedupstream of the valves 36, 38. Preferably, the sensor 47 is located inrelatively close proximity to the engine and is used to measure thepressure downstream from the engine as compared to atmospheric pressure(i.e., the 47 sensor measures the “back pressure” of the system).

The controller can also interface with a temperature sensor 48 thatmeasures the temperature of the exhaust gas emitted from the engine 22.The controller 40 can further interface with pressure sensors (notshown) located on opposite sides of the catalytic converter 34 tomeasure the pressure gradient across the converter 34. The controller 40also can interface with sensors to monitor a variety of other parameterssuch as the speed of the engine (RPM), the rate of acceleration of theengine, the air intake of the engine, air flow exhausted from theengine, the rate at which fuel is supplied to the engine, the air flowrate through each of the flow paths 24, 26, the oxygen concentration inthe exhaust gas, and the length of time of a regeneration cycle of thefilter 32 and engine loading.

While two separate valves 36, 38 have been shown, a single proportionalvalve or other type of valve could also be used. Also, while two outlets28, 30 have been shown, the flow paths 24, 26 could also be outputtedthrough a common outlet. Further, the filter 32 or the catalyticconverter 34 can each be packaged in a muffler (as shown in U.S. Pat.No. 5,355,973 which is incorporated by reference in its entirety) alongwith other structures such as flow distribution arrangements.

II. Proportional Flow to Optimize Filtration While PreventingUnacceptable Backpressure

In the embodiment of FIG. 1, the controller 40 can proportion flow toboth of the flow paths 24 and 26 to control the backpressure of thesystem and to optimize the particulate mass reduction efficiency. Forexample, as the diesel particulate filter 32 becomes loaded or flowrates increase, backpressure of the system may approach a manufacturerset maximum such as 3 inches of mercury. To prevent the backpressurefrom exceeding 3 inches of mercury, the controller 40 can divert aportion of the flow through the catalytic converter 34 while a majorityof the flow is still directed through the diesel particulate filter 32to provide a high particulate mass reduction efficiency. Because thecatalytic converter 34 provides a flow path with significantly less flowrestriction than the filter 32, the backpressure of the system will bereduced by passing at least some of the flow through the catalyticconverter 34.

FIG. 2 shows a particulate material mass reduction efficiency graph fora catalytic converter having an efficiency of 30% and a dieselparticulate filter having an efficiency of 90%. Line 92 shows how flowcan be proportioned between the diesel particulate filter and thecatalytic converter to achieve a net desired particulate material massreduction efficiency in the range of 30-90 percent mass reductionefficiency. For example, to achieve a particulate mass reduction of 30%,all of the mass flow is directed through the catalytic converter 34. Toachieve a particulate mass reduction of 90%, all of the mass flow isdirected through the filter 32. To achieve a particulate mass reductionof 60%, half of the mass flow is directed through the filter 32 and theother half of the mass flow is directed through the catalytic converter34.

III. Reduction of Nitrogen Oxides

The system 20 can also include separate structures for reducing nitrogenoxide (NOx) emissions. For example, in addition to the dieselparticulate filter 32 and the catalytic converter 34, nitrogen oxidereducing structures can be positioned along the first flow path 24, thesecond flow path 26 or along both flow paths 24, 26 upstream ordownstream from the filter 32 and the catalytic converter 34.Alternatively, the diesel particulate filter 32 and the catalyticconverter 34 could themselves be configured for reducing nitrogen oxideemissions. Further, a separate path in parallel with flow paths 24, 26could be equipped with structure for reducing nitrogen oxide emissions.Exemplary structures include selective reduction catalytic converters,lean NOx catalytic converters and NOx traps/absorbers. Examplestructures for reducing nitrogen oxide emissions are disclosed in U.S.Pat. No. 6,182,443 that is hereby incorporated by reference in itsentirety.

For systems configured to reduce nitrogen oxide emissions, the flowpaths 24 and 26 can include structures for injecting chemicals used toenhance NOx conversion. For example, hydrocarbons can be injected forlean NOx catalysts and urea or ammonia can be injected for selectivereduction catalysts.

FIG. 3 shows another system 200 constructed in accordance with theprinciples of the present invention. The system 200 has the sameconfiguration as the system of FIG. 1 except that structures 89 forreducing nitrogen oxide emissions have been provided along the first andsecond flow paths 24, 26.

IV. System with Passive Filter Regeneration

FIG. 4 shows another system 300 constructed in accordance with theprinciples of the present invention. The system 300 has the sameconfiguration as the system of FIG. 1 except no heating structure isprovided for heating the filter 32. Thus, the system 300 uses the heatof the exhaust gas to burn soot from the filter 32 during a regenerationcycle.

V. General System Control Features

In the systems of FIGS. 1, 3 and 4, the controller 40 is preferablyadapted to adjust flow through the flow paths 24 and 26 based on theoperating condition of the filter 32 and the engine 22. For example, toprevent plugging of the filter 32, the controller can be configured toroute flow exclusively through the catalytic converter 34 when theexhaust gas temperature measured at sensor 48 is less than the minimumtemperature (e.g., about 525° F.). When the exhaust gas exceeds theminimum temperature, the controller 40 can route all flow through thefilter 32.

The systems can also include a control feature that routes flow throughthe filter 32 during times of high soot production (e.g., when theengine is rapidly accelerating or rapidly undergoing increased loading).These types of conditions can be detected by monitoring if the rate ofchange of the speed of the engine exceeds a predetermined level, or ifthe time rate of change of flow through the engine exceeds apredetermined level. If a high soot generating condition is detected,flow to the catalytic converter 34 is preferably stopped and all flow isrouted to the filter 32. This sequence preferably overrides the sequencedescribed above such that flow is directed to the filter 32 even if theexhaust temperature is less than the minimum exhaust temperature.

Another consideration addressed by the above systems is loading of thefilter 32. If the pressure sensors detect a backpressure at the filter32 that exceeds a predetermined level (e.g., 3 inches of mercury), thecontroller preferably reduces or stops flow to the filter 32, and opensfrom through the catalytic converter 34. In an active system, a heatercan then be activated to regenerate the filter 32. After regeneration,flow can again be directed though the filter 32. If the system relies onpassive regeneration, the temperature of the exhaust gas will determinewhether regeneration is possible. For example, the system can continueto route flow through the catalytic converter 34 until the temperatureof the exhaust gas exceeds the minimum temperature at which catalysiswill occur at the filter 32 (e.g., about 625° F.). When the exhausttemperature exceeds the catalysis temperature, the controller routesflow back to the filter 32 such that the hot exhaust gas causes thefilter to regenerate via combustion of the soot on the filter.

During regeneration, it is important to maintain a controlled combustionat the filter. To achieve this end, a timer is preferably started at thestart of the regeneration cycle. If the operating conditions of theengine change during a predetermined regeneration cycle period (e.g., 10minutes as determined by the timer) so as to increase the likelihood ofuncontrolled combustion, flow to the filter 32 is preferably stoppedthereby depriving the filter of oxygen for combustion. Example types ofconditions where it would be desirable to stop the regeneration cycleinclude situations where the oxygen content of the exhaust gas exceeds apredetermined level. Typically this might occur if the load on theengine dramatically drops or if the engine is shifted to idle. Highoxygen conditions can be indirectly detected by detecting if thetemperature of the exhaust gas falls below a predetermined level or ifthe speed of the engine falls below a predetermined level. Both of thesefactors can be indicative of a situation in which a high level of oxygenis present in the exhaust gas.

VI. Example Control Logic for System with Passive Filter Regeneration

FIGS. 5A-5L show logic that is indicative of basic controller softwaresuitable for controlling the controller 40 of the passive filterregeneration system of FIG. 4. FIGS. 5A-5E show the logic of a maincontrol loop. FIGS. 5F-5L show sub-routines that branch from the maincontrol loop. FIG. 5L shows an error handling routine.

In the flow chart of FIGS. 5A-5L, process blocks are shown asrectangles. Decision blocks are shown as diamonds. Sub-routines areshown as rectangles with double side walls. Connection points are shownas circles with labels as required.

A number of variables are used in the flow chart. Example variablesinclude back pressure, temperature, RPM and flow. Back pressure ismeasured in the exhaust ducting common to both the diesel particulatefilter 32 and the catalytic converter 34. Temperature is measured in theexhaust flow upstream from the filter 34 and the catalytic converter 32.RPM (i.e., rotations per minute) is measured from the engine. Flow ismeasured in the exhaust flow stream upstream from the separate flowpaths 24, 26.

The flow chart uses a number of flow control variables. For example, theflow chart includes MASTER_STATE variables that control programexecution in the main loop. The MASTER_STATE variables range from level0 to 7. MASTER_STATE level 0 corresponds to a state where the system isoff and waiting for the engine to be started. MASTER_STATE level 1corresponds to an initialization state. MASTER_STATE level 2 correspondsto a BACKPRESSURE RELIEF STATE (i.e., a state where flow is directedthrough the catalytic converter 34 to relieve back pressure).MASTER_STATE level 3 corresponds to a DPF TEMPERATURE ONLINE STATE(i.e., a state where flow is routed through the filter 32 because thetemperature of the exhaust gas is suitable for filtration). MASTER_STATElevel 4 corresponds to a DPF REGENERATION STATE (i.e., a state whereflow is routed through the filter 32 and the temperature of the exhaustgas is suitable to cause active regeneration of the filter).MASTER_STATE level 5 corresponds to a DPF REGENERATION COOL_DOWN STATE(i.e., a state where flow is diverted from the filter to prevent athermal run-away caused by uncontrolled soot combustion at the filter32). MASTER_STATE level 6 corresponds to a DPF_RPM/FLOW ONLINE STATE inwhich the diesel particulate filter is placed online due to operatingconditions that produce high concentrations of soot such as high engineacceleration rates or high flow rate changes. MASTER_STATE level 7corresponds to a SYSTEM FAULT STATE in which an error in the system hasoccurred.

Other flow control variables include BP_STATE, DPF_ONLINE, andREG_COOL_STATE. The BP_STATE variable controls execution of theBACKPRESSURE RELIEF sub-routine. This variable has levels 0-3. TheDPF_ONLINE variable is a Boolean variable that control execution ofdiesel particulate filter calculation routines (e.g., diesel particulatefilter loading, diesel particulate filter duty cycles, mass flow throughthe diesel particulate filter, and particulate material mass reductionefficiencies). The DPF_ONLINE variable is either TRUE (indicating thatall flow is being directed through the filter 32) or FALSE (indicatingthat all flow is not being directed through the filter 32). TheREG_COOL_STATE variable controls the execution of the regeneration cooldown sub-routine. This variable has levels 0-2.

The flow chart also utilized a number of constants. The constantsinclude:

-   -   TEMP_ENGINE_MIN: the minimum temperature that the controller        considers necessary for operation (e.g., about 150° F.);    -   BP_MAX: the maximum back pressure allowed by the engine        manufacturer (e.g., about 3 inches Hg);    -   RPM_MIN: the minimum rpm indicative of a running engine (e.g.,        about 500)    -   TEMP_LOW: the minimum temperature allowed for exhaust flow to be        directed through the diesel particulate filter (e.g., about 525°        F.);    -   T_CATALYSIS: the minimum temperature at which catalysis actively        occurs (e.g., about 625° F.);    -   RPM_ACCEL: the minimum engine annular acceleration for an engine        accelerating under load (e.g., about 200 rpm/s);    -   FLOW_ACCEL: the minimum engine exhaust flow for an engine        accelerating under load (e.g., about 200 cfm/s);    -   LOADING_MAX: the maximum diesel particulate loading that is        allowed before a system fault is entered;    -   BP_TIMER_MAX: the maximum time period allowed in the back        pressure relief state (e.g., about 15 seconds); and    -   T_CATALYSIS_LOW: the lower temperature limit used to exit from        the diesel particulate filter regeneration state (e.g., about        450° F.).

A. Main Loop

This section described the initialization sequence of the controller.During this description, it is assumed that no operating conditions arepresent that would cause flow to be directed through the filter 32.

Referring to FIG. 5A, the flow chart starts at oval 600. As shown byrectangle 602, the system is initially set to MASTER_STATE level 0 whilethe system waits for indication that the engine has been started. Duringthis time period, the diesel particulate filter and catalytic convertervalves are both open as indicated by parallelogram 604. The systemremains at MASTER_STATE level 0 until the system detects that thetemperature of the exhaust gas is greater than TEMP_ENGINE_MIN or therpm is greater than RPM_MIN (see diamond 606).

Once the system has detected that the engine has started, the system isset to MASTER_STATE level 1 as indicated by block 608. Also, theBP_STATE variable is set to level 0 and the DPF_ONLINE variable is setto FALSE as indicated by block 610. With the MASTER_STATE variable setat level 1, the routine proceeds through diamond 612 (shown at FIG. 5B)to the DPF_OFFLINE state indicated by rectangle 614. The sub-routinecorresponding to the DPF_OFFLINE state is shown at FIG. 5G. In thesub-routine, the catalytic converter valve is opened and the dieselparticulate filter valve is closed as indicated by parallelogram 616.Also, the BP_STATE is again set to level 0 and the DPF_ONLINE state isagain set to false as indicated by block 618. At the completion of thesub-routine of FIG. 5G, flow returns to diamond 620 of the main loopthat is shown at FIG. 5B.

Diamond 620 inquires if the backpressure of the system is greater thanBP_MAX. If the backpressure does not exceed BP_MAX, flow proceeds todiamond 622. If the backpressure does exceed BP_MAX, flow proceeds torectangle 621 where the MASTER_STATE variable is set to level 2corresponding to the back pressure relief state. From rectangle 621,flow proceeds to diamond 622.

Diamond 622 inquires whether the MASTER_STATE variable is at level 2. Ifthe variable is at level 2, flow proceeds to block 623, whichcorresponds to the BACKPRESSURE RELIEF STATE. The subroutinecorresponding to the BACKPRESSURE RELIEF STATE is shown at FIG. 5 f. Ifthe MASTER_STATE variable is not at level 2, the logic will proceed todiamond 624 (shown at FIG. 5C).

Diamond 624 inquires whether the MASTER_STATE variable is at level 4. Ifthe MASTER_STATE variable is at level 4, flow proceeds to rectangle 626that represents the DPF_REGENERATIONSTATE. The sub-routine for theDPF_REGENERATIONSTATE is shown at FIG. 5I. If the MASTER_STATE variableis not at level 4, flow proceeds from diamond 624 to diamond 628.

Diamond 628 inquires whether the MASTER_STATE variable is at level 5. Ifthe MASTER_STATE variable is at level 5, flow is directed to rectangle630 corresponding to the regeneration COOL_DOWN STATE. The sub-routinecorresponding to the regeneration COOL_DOWN STATE is shown at FIG. 5J.If the MASTER_STATE variable at level 5, flow proceeds to from diamond628 to diamond 632.

Diamond 632 inquires whether the MASTER_STATE variable is at level 6. Ifthe MASTER_STATE variable is at level 6, flow proceeds to block 634corresponding to the DPF_RPM-FLOW ONLINE STATE. The sub-routinecorresponding to the DPF_RPM-FLOW ONLINE STATE is shown at FIG. 5K. Ifthe MASTER_STATE variable is not at MASTER_STATE level 6, flow proceedsfrom diamond 632 to diamond 636.

Diamond 636 inquires whether the MASTER_STATE variable is at level 3. Ifthe MASTER_STATE variable is at level 3, flow proceeds to rectangle 638corresponding to the DPF_TEMPERATURE ONLINE STATE. The subroutinecorresponding to the DPF_TEMPERATURE ONLINE STATE is shown at FIG. 5H.If the MASTER_STATE variable at level 3, flow proceeds to from diamond636 to diamond 640 on page SD.

Diamond 640 inquires whether the temperature is greater thanT_CATALYSIS. If the temperature is greater than T_CATALYSIS, theMASTER_STATE variable is changed to level 4 as indicated at rectangle642. Otherwise, the logic will proceed to diamond 644.

Diamond 644 inquires whether the DPF_ON_LINE variable is set to TRUE(i.e., the logic checks whether all flow is being directed through theparticulate filter). If the DPF_ON_LINE variable is not set to TRUE, thelogic checks whether the exhaust system is in a condition in which itwould be suitable or desirable to direct flow through the filter 32. Forexample, diamond 646 inquires whether the time rate of change of RPM isgreater than RPM_ACCEL, diamond 648 inquires whether the time rate ofchange of flow is greater than FLOW_ACCEL and diamond 650 inquireswhether the temperature is greater than the TEMP_LOW. If the answer tothe question presented in either diamond 646 or diamond 648 is yes, theMASTER_STATE variable is changed to level 6 as indicated by rectangles652 and 654. If the answers to the inquiries set forth by diamonds 646and 648 are no, the logic proceeds to diamond 650. If the answer to theinquiry of diamond 650 is yes, the MASTER_STATE variable is set to level3 as indicated by rectangle 656. If the answer to the inquiry of diamond650 is no, flow proceeds to diamond 658 shown on FIG. 5E.

Diamond 658 inquires whether a system error has occurred. If a systemerror has occurred, the MASTER_STATE variable is set to level 7 at box660 and the SYSTEM FAULT STATE sub-routine of FIG. 5L is implemented atbox 662. If no system error has occurred, flow proceeds to diamond 664.

Diamond 664 inquires whether the DPF_ON_LINE variable is set to TRUE. Ifthe DPF_ON_LINE variable is set to TRUE, the controller calculates theloading of the DPF as indicated at box 666. Diamond 668 then inquireswhether the DPF loading is equal to or greater than loading max (e.g.,the loading where the diesel particulate filter can no longer beregenerated using only passive techniques). If the answer to the inquiryof diamond 668 is yes, flow proceeds to box 660 where the MASTER_STATEvariable is set to level 7. If the answer to diamond 668 is no, a dieselparticulate filter duty cycle is calculated at box 670 and the averagemass flow through the diesel particulate filter is calculated at box672. From box 672, flow proceeds to box 674 where variables such asflow, rpm, back pressure and temperature are updated. From box 674, flowproceeds back to diamond 612 of FIG. 5B and the main loop of the routineis repeated.

B. Backpressure Relief

The flow chart of FIGS. 5A-5L includes a subroutine loop for preventingexcessive backpressure in the system. For example, if the backpressurein the system exceeds BP_MAX, diamond 620 (see FIG. 5B) of the main loopdirects the control logic to rectangle 621 where the MASTER_STATEvariable is set to level 2. With the MASTER_STATE variable set to level2, flow proceeds through diamond 622 to rectangle 623 where the backpressure relief sub-routine of FIG. 5F is implemented. Within thebackpressure relief subroutine, the DPF_ON_LINE variable is set to FALSEat box 700. Diamond 702 then inquires whether the BP_STATE variableequals 0. If the BP_STATE variable equals 0, the logic proceeds to box704 where the FLOW_IN variable is set to the real-time exhaust flowvalue of the exhaust system. Thereafter, a BP_TIMER value is set to amaximum value (e.g., 15 seconds) at rectangle 706. Flow is then openedto both the catalytic converter 34 and the diesel particulate filter 32at parallelogram 708. The BP_STATE variable is then set to 1 atrectangle 709 and flow proceeds back to the main loop.

In the next cycle through the main loop, since the MASTER_STATE variableremains set at level 2, flow is again directed to the back pressurerelief sub-routine of FIG. 5F. Since the BP_STATE variable haspreviously been set to 1, flow proceeds through diamond 702 to diamond712. From diamond 712, flow proceeds to a count-down leg of thesubroutine that includes box 714 where the BNP_TIMER value isincremented down by 1 unit. After the timer value has been incrementeddown by 1 unit, flow proceeds to diamond 716, which inquires whether theBP_TIMER value equals 0. The logic flow will continue be cycled betweenthe main loop back and the count-down leg of the subroutine until theBP_TIMER value equals 0. When this occurs, the BP_STATE value is set to2 at rectangle 717. Logic flow then returns to the main loop.

With the BP_STATE value set to 2, the next time through the subroutinethe flow proceeds through diamond 712 to diamond 718. Diamond 718inquires whether the BP_STATE value equals 2. If the answer is yes, flowproceeds to diamond 720. Diamond 720 inquires whether the currentexhaust flow through the system is less than or equal to a portion(e.g., 85%) of the FLOW_IN value. If the answer is yes, the BP_STATEvalue is set to 3 at box 722. By setting the BP_STATE value to 3, thenext time through the sub-routine flow will proceed downwardly throughdiamond 718 to rectangle 724. At rectangle 724, the BP_STATE value isset to 0Next, at rectangle 726, the MASTER_STATE variable is set to 1and the sub-routine is complete. If the answer to diamond 720 is no,flow continues to cycle between the subroutine and the main loop.

The timer feature described above provides the system with sufficienttime for the operating condition of the system to change before thecontrol logic attempts to reopen the diesel particulate filter. Thisprevents valves from being opened and closed in rapid succession. Also,if the total flow through the system hasn't dropped during the periodset by the timer, it is unlikely that backpressure in the system wouldhave been reduced. Thus, diamond 720 prevents the system from stoppingthe backpressure relief sub-routine until the system determines thatflow through the system has dropped by a predetermined factor.

C. DPF Regeneration State

If the temperature of the exhaust gas is greater than T_CATALYSIS asinquired by box 640 on FIG. 5D, rectangle 642 sets the MASTER_STATEvariable to level 4. With the MASTER_STATE variable set to level 4,diamond 624 of the main loop (see FIG. 5C) causes the regenerationsub-routine to be implemented at rectangle 626. The regenerationsub-routine is shown at FIG. 5I. In the regeneration sub-routine,diamond 750 inquires whether the temperature of the exhaust gas is lessthan T_CATALYSIS_LOW. If the answer is no, the valve to the dieselparticulate filter is opened and the valve to the catalytic converter isclosed. By opening flow to the filter, the hot exhaust gas travelingthrough the diesel particulate filter causes combustion of soot on thefilter thereby allowing the filter to regenerate. After the dieselparticulate filter has been opened and the catalytic converter closed,the BP_STATE variable is set to 0 and the DPF_ON_LINE variable is set toTRUE at box 754.

The DPF_REGENERATIONSTATE continues unless the temperature of theexhaust gas falls below the T_CATALYSIS_LOW value. The low temperatureis indicative of a situation in which high oxygen content in the exhaustgas could cause a thermal run away at the filter. When a temperatureless than T_CATALYSIS_LOW is detected, the MASTER_STATE variable is setto level 5 and the REG_COOL_STATE value is set to 0 at box 756 of theregeneration subroutine.

With the MASTER_STATE value set to 5, diamond 628 of the main loop (seeFIG. 5C) will cause the REGENERATION COOL_DOWN sub-routine to beinitiated at box 630. The REGENERATION COOL_DOWN subroutine prevents athermal runaway from occurring by stopping exhaust flow to theparticulate filter. The REGENERATION COOL_DOWN subroutine is shown atFIG. 5 j. At parallelogram 800 of the REGENERATION COOL_DOWN subroutine,flow to the diesel particulate filter is stopped and rerouted to thecatalytic converter. At rectangle 802 the DPF_ON_LINE variable is set toFALSE. Flow then proceeds to diamond 804, which inquires if theREG_COOL_STATE is set to 0. Since this value was set to 0 during theDPF_REGENERATION sub-routine of FIG. 5I, flow proceeds to rectangles 806and 807 where the COOLDOWN_TIMER is set to COOL_MAX (e.g., 20 seconds)and the REG_COOL_STATE is set to 1. The sequence then proceeds backthrough the main loop and returns to the regeneration sub-routine.

Upon return to the regeneration sub-routine of 5J, the logic flows todiamond 808. Diamond 808 asks whether the REG_COOL_STATE equals 1. Sincethis variable was set to 1 at box 807, flow proceeds to a timercountdown leg of the subroutine that includes box 810 where theCOOLDOWN_TIMER value is sequenced down by 1 unit. Diamond 812 theninquires whether the COOLDOWN_TIMER value equals 0. The logic willcontinue to be cycled between the main loop and the timer countdown legof the subroutine until the COOLDOWN_TIMER has been sequenced to 0. Whenthe COOLDOWN_TIMER has been sequenced to 0, flow moves to rectangle 814,which sets the REG_COOL_STATE value to 2. With the REG_COOL_STATEvariable set to 2, during the next pass through the COOL_DOWN subroutineflow will move through diamond 808 to rectangle 816. At rectangle 816,the REG_COOL_STATE is set to 0 and the MASTER_STATE variable is set tolevel 1. The regeneration COOL_DOWN state is then complete. Preferably,the timer of the sub-routine is sufficiently long to ensure thatcombustion at the diesel particulate filter has been extinguished.

D. DPF RPM/Flow Online State

If the system detects a condition indicative of a high rate of sootcondition (e.g., rapid acceleration of the engine or a rapid change inthe rate of flow through the exhaust system), the MASTER_STATE variableis set to level 6 (see diamonds 646 and 648 and blocks 652 and 654 ofFIG. 5D). With the system set at MASTER_STATE level 6, diamond 632 ofthe main loop (see FIG. 5C) causes the DPF_RPM/FLOW ONLINE STATEsub-routine of block 634 to be initiated. This sub-routine is shown atFIG. 5K. Upon entering the sub-routine, diamond 900 checks to ensurethat the high soot generating condition is still present. If thecondition is not present, flow is directed to rectangle 902 where thesystem is reset to MASTER_STATE level 1. If the high soot productioncondition is present, flow proceeds from diamond 900 to parallelogram904. At parallelogram 904, the diesel particulate filter is opened andthe catalytic converter is closed so that filtration takes place. Also,at block 905, the BP_STATE is set to 0 and the DPF_ON_LINE state is setto TRUE.

It will be appreciated that the DPF_RPM/FLOW ONLINE STATE sub-routineallows for filtration during high soot producing periods even if thetemperature of the exhaust gas is relatively low. It will also beappreciated that other sub-routines such as the BACKPRESSURE RELIEFsub-routine, the DPF REGENERATION subroutine and REGENERATION COOL_DOWNsubroutine have priority in sequence over the DPF_RPM/FLOW ONLINEsub-routine.

E. DPF Temperature Online State

The DPF_TEMPERATURE ONLINE subroutine is preferably adapted to turn thediesel particulate filter online when the exhaust temperature exceedsTEMP_LOW. For example, referring to diamond 650 and block 656 of FIG.5D, when the exhaust temperature exceeds TEMP_LOW, the MASTER_STATEvariable is set to level 3. With the MASTER_STATE variable set to level3, diamond 636 on FIG. 5C of the main loop causes implementation of theDPF_TEMPERATURE ONLINE subroutine as indicated by block 638. Thesub-routine for the DPF_TEMPERATURE ONLINE state is shown at FIG. 5H.Diamond 920 within the DPF_TEMPERATURE ONLINE sub-routine inquireswhether the temperature is greater than TEMP_LOW. If the temperature isnot greater than TEMP_LOW, the MASTER_STATE variable is reset to 1 (seerectangle 922) and the sub-routine is terminated. If the temperature isgreater than TEMP_LOW, the diesel particulate filter valve is opened andthe catalytic converter valve is closed at parallelogram 924. Also, theBP_STATE variable is set to 0 and the DPF_ONLINE variable is set to trueat rectangle 926. Flow then returns to the main loop.

F. System Fault

If a system error is detected at diamond 658 of the main loop (see FIG.5E), the MASTER_STATE variable is set to 7 at box 660. Similarly, if itis detected at diamond 668 that the DPF loading is greater than or equalto LOADING_MAX, the MASTER_STATE variable is also set to 7. Once theMASTER_STATE variable is set to 7, the system fault sub-routine isinitiated at block 662. The system fault sub-routine is shown at FIG.5L. Within the sub-routine, diamond 950 inquires whether a controllersystem fault has occurred. Also, diamond 952 inquires whether DPFloading is greater than or equal to LOADING_MAX. If the answer to eitherof the questions presented at diamonds 950 and 952 is yes, thesub-routine proceeds to parallelogram 954 where the diesel particulatefilter valve is closed and the catalytic converter valve is opened.Thereafter, a fault light is turned on at parallelogram 956 and an errorcode is transmitted at parallelogram 958. The system is then disabled.

If the answers to the inquiries presented at diamonds 950 and 952 areno, the MASTER_STATE variable is reset to 1 at rectangle 960 and theroutine returns to the main loop.

VII. Packaging Arrangement

FIGS. 6A and 6B show a packaging arrangement 100 for packaging thesystem 20 of FIG. 1. The arrangement 100 includes an oval muffler body102 (i.e., a muffler shell) having an inlet 104 and an outlet 106. Whilenot shown, the inlet 104 can include structures for attenuating soundand for distributing flow. Valves 36 and 38 are mounted adjacent theinlet end of the muffler body 102. An oval valve plate 108 is mountedwithin the muffler body 102. The valve plate 108 defines openings 109and 110 that are respectively opened and closed by the valves 36 and 38.The perimeter of the plate 108 is preferably welded to the muffler body102 with a continuous connection (e.g., a continuous weld bead) so as toform an airtight seal. Oval mounting plates 112 are mounted within themuffler body 112 downstream from the valve plate 108. The mountingplates 112 define openings 113 and 114 in which the diesel particulatefilter 32 and the catalytic converter 34 are respectively mounted. Thediesel particulate filter 32 includes an outer casing 116 that extendstoward the inlet end of the muffler body 102 and is welded to the valveplate 108. The first flow path 24 extends through the casing 116 and thesecond flow path 24 is defined by the region of the muffler body 102located outside of the casing 116. The mounting plates 112 preferablyseal the muffler body 102 such that flow cannot exit the muffler body102 without passing through either the catalytic converter 34 or theparticulate filter 32.

FIG. 6C shows a packaging arrangement 100′ that is the same as thepacking arrangement of FIGS. 6A and 6B except that the arrangement has aside inlet 104′ and a side outlet 106′. As shown the inlet 104′ and theoutlet 106 are offset 180 degrees relative to one another. It will beappreciated that the inlet and the outlet can be offset at any number ofdifferent angles relative to one another to correspond to differentexhaust system configurations. In other embodiments the system, thesystem could include an axial inlet and a side outlet or a side inletand an axial outlet.

It will be appreciated that other components of the system (e.g.,pressure and temperature sensors and the heating element) can also beincorporated within the muffler body 102. It will further be appreciatedthat structures for reducing nitrogen oxide emissions can also beincorporated into the muffler body.

VIII. Multi-Filter Embodiment and Corresponding Packaging Arrangement

FIG. 7 shows another system 400 constructed in accordance with theprinciples of the present invention. The system 400 has the sameconfiguration as the system of FIG. 1 except an additional flow path 80parallel with flow paths 24 and 26. Flow path 80 includes an additionaldiesel particulate filter 32, a heater 42, a pressure sensor 46 and avalve 36. Based on the operating condition of the system, the controller40 can route flow to the different flow paths 24, 26 and 80. Forexample, if the filter 32 of the first flow path 24 is plugged, flow canbe re-routed through path 80 until the plugged filter 32 of flow path 24regenerates.

FIGS. 8A and 8B show a packaging arrangement 500 for packaging thesystem 400 of FIG. 7. The system 500 has the same configuration as thesystem of FIGS. 6A and 6B except for the addition of the third flow path80 within muffler body 502. The system 500 includes two mounting plates512 each having 3 separate openings for respectively mounting the twofilters 32 and the converter 34. The system also includes a valve plate508 having openings corresponding to the two valves 36 and the valve 38.Also, the arrangement includes a side inlet 504 and an axial outlet 506.The flow paths 24 and 26 are isolated from each other and the flow path80 by extending the casings 116 of the filters 32 to the valve plate508.

FIG. 8C shows a packaging arrangement 500′ that is the same as thepacking arrangement of FIGS. 8A and 8B except that the arrangement has aside outlet 506′.

It will be appreciated that the embodiments described herein are merelyexemplary. For example, the various constant values provided herein arefor illustration purposes only, and may vary from system to system andcatalyst to catalyst. Since many embodiments of the invention can bemade without departing from the spirit and scope of the invention, theinvention resides in the claims hereinafter appended.

1. An exhaust treatment system for treating exhaust gas, the systemcomprising: a first flow path including a particulate filter; a secondflow path including a catalytic converter; a valve arrangement forcontrolling flow to the first and second flow paths; and a controllerthat interfaces with the valve arrangement to modify flow between thefirst and second flow paths in response to changes in the operatingconditions of the system.
 2. The system of claim 1, wherein thecontroller proportions flow between the first and second flow paths. 3.The system of claim 1, wherein the controller opens and closes flow tothe first and second flow paths.
 4. The system of claim 1, wherein thecontroller directs flow to the second flow path when a backpressure ofthe system exceeds a predetermined value.
 5. The system of claim 1,wherein the particulate filter has a particulate mass reductionefficiency greater than 80 percent.
 6. The system of claim 5, whereinthe catalytic converter has a particulate mass reduction efficiency lessthan 50 percent.
 7. The system of claim 1, wherein the catalyticconverter and the particulate filter are mounted in a single housing. 8.The system of claim 7, wherein the single housing comprises a mufflershell.
 9. The system of claim 1, further comprising a structurepositioned along at least one of the first and second flow paths forreducing nitrogen oxide emissions.
 10. The system of claim 1, furthercomprising a temperature sensor for measuring exhaust temperature thatinterfaces with the controller, wherein the controller directs flow tothe second flow path when the temperature of the exhaust gas is lessthan a predetermined temperature, and wherein the controller directsflow to the first flow path when the temperature of the exhaust gasexceeds the predetermined temperature.
 11. The system of claim 10,wherein the exhaust gas is generated by a diesel engine, wherein thecontroller monitors an operating condition of the engine to detect acondition indicative of high soot production, and wherein the controllerdirects flow to the first flow path when a condition indicative of highsoot production is detected even if the temperature is less than thepredetermined temperature.
 12. The system of claim 1, wherein theexhaust gas is generated by a diesel engine, wherein the controllermonitors an operating condition of the engine to detect a conditionindicative of high soot production, and wherein the controller directsflow to the first flow path when a condition indicative of high sootproduction is detected.
 13. The system of claim 3, further comprising aheating device for regenerating the particulate filter.
 14. The systemof claim 13, wherein the heating device includes an electric heatingelement.
 15. The system of claim 13, wherein the heating device includesa diesel fuel burner.
 16. The system of claim 1, wherein the controllerdirects flow to the first flow path when a temperature of the exhaustgas exceeds a predetermined level to promote passive regeneration of theparticulate filter.
 17. The system of claim 16, wherein the controllersuppresses regeneration of the particulate filter if a conditionindicative of a detrimental regeneration is detected.
 18. The system ofclaim 17, wherein the controller suppresses detrimental regeneration ofthe particulate filter by closing flow to the first flow path.
 19. Anexhaust treatment system for treating exhaust gas, the systemcomprising: a first flow path including a particulate filter; and asecond flow path including a catalytic converter, the second flow pathand the first flow path being arranged in parallel relative to oneanother.
 20. The exhaust treatment system of claim 19, furthercomprising a muffler shell in which both the catalytic converter and theparticulate filter are mounted.
 21. A method for treating exhaust gasusing a system including a catalytic converter and a particulate filter,the method comprising; modifying flow provided to the catalyticconverter and the particulate filter in response to operating conditionsof the system.
 22. The system of claim 13, wherein the controllersuppresses regeneration of the particulate filter if a conditionindicative of a detrimental regeneration is detected.
 23. The system ofclaim 22, wherein the controller suppresses detrimental regeneration ofthe particulate filter by closing flow to the first flow path.